Walt and Jesse need power to jumpstart their RV, so they create battery cells in order to generate current. Walt explains to Jesse how their creation, although it looks unconventional, will be a functional battery. He lists some of the components of a battery and how they are making each.
Beakman uses ping pong balls to simulate electrons. He rolls them down a pipe that gets narrower so they pile up (resistance). In a light bulb, the resistance causes the coil to heat up and make light.